Traditional wet chemistry techniques in analytical chemistry and its use in the area of clinical chemistry have in the recent decades been improved. The improvements are based on the interaction of microprocessors with electromechanical devices that allow for these measurements to be made more precisely and easily.
In the subdiscipline of electrochemical measurements in the recent decade there has been considerable adaptation of the above methods to develop units that can self calibrate and measure the components in a sample. These units have been called cards or cartridges.
With the movement of chemistry tests outside the ambiance of a laboratory the need for these self contained test units for a wide variety of tests becomes important. Hence the need for a universal card or cartridge designed to be able to be modified at the factory to carry out a given range of tests which can work with one instrument becomes defined. At the factory the requisite range is fixed as according to customer requirements. Hence there will be cartridges that can carry out ionic profiles in soil or blood, and so on. To be able to carry out a wide range of tests it becomes important that the cartridge together with the instrument could lend themselves to a number of wet chemistry techniques ranging from electrochemical to optical methods.
The invention relates to a disposable universal sensor cartridge and an analyzer that can carry out a fixed range of tests that may use more than one method of analysis at the same time or different methods from time to time depending on the cartridge and the tests prescribed to it. Although the cartridge could work with a conventional reference electrode or source it specially lends itself for use with the comparator method developed by Guruswamy (patent application Ser. No. 07/008,554 to be U.S. Pat. No. 4,762,594 on Aug. 9, 1988) which does not require a reference electrode or source but rather a comparator electrode or source.
In clinical chemistry it is important for samples drawn from different parts of the body by devices ranging from "lancets" for finger pricks or finger sticks to acquire single drops of blood, to syringes for venous blood samples to be introduced easily into the cartridge with minimum contamination or evaporative loss from the sample. Our invention relates among other things to the drawing of blood from a punctured finger via a finger prick into the cartridge directly while allowing for other modes of introduction into the cartridge.
Most analytical systems are exposed to the ambient environment. They are not airtight. An airtight environment is desirable, first, to more closely match in-vivo conditions. Furthermore, it is important, for example, in blood gas analysis to avoid sample contamination from air so as to cause skewing of the results. This is particularly true in the analysis of blood gases but may pertain to measurement of other components as well. Lastly, to obtain a series of substance or component measurements from a sample, requires considerable time and many individual measurements. Not only is the time factor detrimental but, also, specimen contamination and chemical changes in the specimen are likely to occur. Hence, it is desirable to maintain an airtight measuring environment to achieve accurate measurements of certain substances, and most notably, blood gas concentrations. Lastly, most known systems do not contemplate fixing or providing fixed volume delivery. Elaborate stirring or mixing arrangements are used to insure uniform transport to the sensor. It would be desirable to conduct measurements of a fixed volume of solution and especially desirable to provide analysis requiring only a small volume of solution uniformly delivered to the sensor to make the measurements.
Other practical considerations arise relative to laboratory use by the clinician. In the event that a system is intended to be reusable, it is incumbent upon the operator or technician to insure that the electrodes are not contaminated when preparing for a test. Thorough cleaning and recalibration is necessary for each use. Such efforts require considerable labor and render cost ineffective the use of reusable systems especially in hospital laboratories or make inefficient their use in the field. Where disposable systems are employed, problems arise relating to the technician's reproducibility of the technique used.
Another aspect of electrochemical apparatus design and operation that has escaped attention in developments to date is the attribute of a compact, simply employable, field or laboratory use instrument which can be operated by persons having a minimum of skilled training. Miniaturized and standardized equipments are not available for providing analytical electrochemical measurements like those described above.